The present invention relates to a motor control device and a motor system.
Brushless motors which are popularly utilized as motors of electrical equipments have been operated with pulse width modulation (PWM) sine-waves for wide-range variable speed control and power consumption reduction. In addition, for the sake of cost reduction and miniaturization, sensorless operation has been performed while detecting the rotation position of the brushless motor without utilizing a position sensor such as a Hall element.
It has been known that an arithmetic process of current control and an arithmetic process of magnetic pole position estimation are alternately performed every half period by dividing PWM carrier waves (for example, see JP-A 2003-33075 (KOKAI)). Motor current information is utilized for these arithmetic processes. The motor current information is acquired by performing A/D conversion on voltage generated at a shunt resistance.
For example, a three-shunt type has A/D converters corresponding to each of U-phase, V-phase and W-phase. Since the voltage generated at the shunt resistance is possible to be acquired only when a lower switch of a driver of each of the three phases is kept ON, the A/D converters are required to perform A/D conversion within a short time of the order of several micro seconds. For example, in a case that the PWM switching frequency is 18 kHz and the duty is 90%, the OFF time of the lower switch is 5 μs. Accordingly, three channels of high-speed A/D converters are to be arranged and a problem of increasing a circuit area has occurred.
Further, it is known to configure to arrange one channel of the A/D converter and to provide shunt resistance voltage of each phase to the A/D converter with switching by a multiplexer. With this configuration, the A/D converter performs A/D conversion within a short time when the driver lower switch of each of three phases is kept ON while the shunt resistance voltage for three phases is switched by the multiplexer. Therefore, the A/D converter is required to perform A/D conversion in extremely high speed and a problem of increasing cost occurs.